The present invention relates to a two component room temperature vulcanizable silicone rubber composition and more particularly the present invention relates to two component or two package room temperature vulcanizable silicone rubber compositions for the coating of automotive parts to protect them from corrosion.
Two component room temperature vulcanizable silicone rubber compositions are well-known. Generally such compositions comprise a base silanol end-stopped diorganopolysiloxane polymer having a viscosity of anywhere from 500 to 500,000 centipoise at 25.degree. C.; an alkyl silicate or partial hydrolysis product of an alkyl silicate as a cross-linking agent and a metal salt of a carboxylic acid with the metal ranging from lead to mangense in the Periodic Table as the curing catalyst. There may be also incorporated into such composition reinforcing and extending fillers. Examples of reinforcing fillers are, for instance, fumed silica, precipitated silica. Examples of extending fillers are, for instance, iron oxide, zinc oxide, diatomaceous earth, ground silica and so forth. Other agents that may be added to the composition are anti-settling agents such as hydrogenated castor oil and self-bonding additives. An example of a self-bonding additive for a two-component room temperature vulcanizable silicone rubber composition is an amino functional silane such as gamma amino propyl triethoxy silane. An example of such a self-bonding additive is, for instance, to be found in the U.S. Patent of Warren Lampe et al, U.S. Pat. No. 3,888,815 which is hereby incorporated by reference into the present case.
In preparing the composition, normally the silanol polysiloxane is packaged separately from the cross-linking agent and the metal salt of a carboxylic acid is usually packaged with the cross-linking agent. The filler and the other ingredients are usually incorporated into the silanol end-stopped polymer. Accordingly, the silanol polymer with the filler and other ingredients is usually packaged in a separate package and the alkyl silicate cross-linking agent and the metal salt of a carboxylic acid usually packaged in a second package. There is formed a two-package or two component room temperature vulcanizable silicone rubber composition, (hereinafter referred to as an RTV silicone composition). When it is desired to cure the composition, the two components are simply mixed together and allowed to cure either in the presence or absence of atmospheric moisture to a silicone elastomer. Normally a tack-free coat will form from 20 to 60 minutes after the two components are mixed and applied and the composition will be essentially cured in 24 to 72 hours after mixing. To hasten the cure of the composition, and especially to obtain deep section cure, there may be incorporated into the composition small amounts of water, in either of the two packages. There have been developed mixing nozzles for applying the two components or mixing the two components simultaneously and spraying them on to various surfaces, for instance, on roofs. There are also certain of these two component room temperature vulcanizable silicone rubber compositions, which are dissolved in organic hydrocarbon solvents such as cyclohexane, cycloheptane, cyclooctane, mineral spirits, toluene, that is, both components are dissolved in solvents and applied by a spray mixing nozzle on surfaces so as to form a thin coating. As soon as the composition is sprayed, the solvent gradually evaporates away and then the composition appears to form a thin layer of silicone elastomer at room temperature. The two components can be applied after mixing by spraying, brushing or dipping. Irrespective of how the two compositions are mixed and applied, it will cure to a silicone elastomer and depending on the amount of filler and the type of filler and other ingredients, it will have a desirable tensile strength and even to some extent be abrasion resistant. It will also have an elastomeric properties of a silicone rubber and have a certain amount of elongation, a good tear, and a good hardness. Such compositions have been utilized traditionally to form, for instance, silicone molds, from which plastic parts are fabricated. This is because of high tear strength of the silicone elastomer and its anti-adhesion properties. These compositions because of their resistance to moisture in the cured state and the elements as well as being resistant to degradation from ultraviolet light, have been utilized for encapsulated of potting composition. They also have found wide use as stated before for roof compositions.
At one time they were utilized as sidewalk or traffic toppings; however, the composition did not have a sufficient abrasion resistance at that time to be suitable as a traffic topping. Accordingly, such silicone compositions have wide use where an RTV cure is desirable and where physical properties have resistance to the elements and moisture, good electrical properties as well as anti-stick properties or good high temperature properties commesurate with good low temperature properties are desired. It should also be appreciated that the composition is relatively cheap to prepare as compared with most RTV silicone rubber compositions. Such compositions were utilized to fabricate gaskets and oil resistance parts in automobiles. However, the compositions were never properly evaluated as far as is known to the reader for their corrosion resistant properties.
Recently, because of energy restrictions, cars have been required to have greater and greater gas mileage. To accomplish this purpose, automobiles have been made smaller and of lighter weight. In particular, parts in the automobile have been fabricated with lighter gauge metal and of smaller total weight. It was desired as the weight of automobiles and the weight of metal parts in the automobile have been decreased to thus increase the gas consumption of the automobile. Accordingly, it has become necessary to find means to protect the automobile from corrosion for as long a period of time as prior heavier metal parts accomplished. At the same time, it was desirable to utilize a coating which would be relatively inexpensive. It should be noted by relatively inexpensive it is meant that in the past RTV compositions were too expensive to utilize as coatings for the parts of automobiles. However, as the cost of the overall automobile increased and as the premium that the consumer paid for gasoline increased, many more materials have become competitively desirable to utilize as protective coatings for the lighter gauge metal parts that are placed in the present day automobile. Accordingly, various types of coatings have been attempted for lighter gauge metal parts of automobiles such as the coating of the underside of the automobile to protect it from corrosion; the coating of tailpipes to protect them from corrosion; and the coating of mufflers and resonators to protect them from corrosion.
However, while some of these coatings which were the most desirable in that they protected the underlying metal from corrosion were light in weight, thus fulfilling the requirements of increasing the gas economy of the present day automobiles, nevertheless, they had one disadvantage, they were hard brittle coatings and when they were hit by a stone, they would break or chip off, allowing the undercoating metal to be exposed to the corrosive elements. Accordingly, it was highly desirable to find a competitive corrosion protecting coating which would be competitively priced with other coatings and yet be more durable and tenacious as far as adhering and protecting the metal parts from corrosion.
Accordingly, it is one object of the present invention to provide for a two component RTV composition for coating the underside of automobiles, for coating tailpipes and for coating mufflers so as to protect them from corrosion.
It is an additional object of the present invention to provide for a two component RTV silicone composition which can be applied as a thin layer to the underside of an vehicle to protect it from corrosion and yet at the same time not chip off when hit by a hard stone.
It is a still additional object of the present invention to provide for a two component RTV silicone composition coating for mufflers and tailpipes such that it will protect the mufflers and tailpipes from corrosion and yet the coating will be in an elastomeric form which will not be brittle and chip off when hit by a sharp object.
It is still yet an additional object of the present invention to provide a method for coating the undersides of vehicles, for coating mufflers, and for coating tailpipes with a two-component RTV silicone composition to protect the tailpipes, the underside of vehicles from corrosion. These and other objects of the present invention are accomplished by means of the disclosures set forth hereinbelow.